SULPHATE CONTENTS IN
WATER SOIL(2:1) EXTRACT
● Water soil extract
● Procedure of the experiment
WHAT ARE SULPHATES
● The sulphate ion is a polyatomic anion with the
empirical formula so2-
● Acid sulphate soils are naturally occurring soils,
sediments or organic substrates (e.g. peat) that
are formed under waterlogged conditions.
● Soils containing large amount of sulphates, when
exposed to air or water form sulphuric acid.
● This acid furthur lead to release of heavy metals
and both these acid and heavy metals lead to
● Killing vegetation, degrading groundwater,
degrading the quality of soil.
● Sulphates may also enter the food chain and may
have adverse effect on bodiversity.
EFFECTS OF SULPHATES FROM
ENGINEER VIEW POINT
Presence of sulphates poses problem for a civil
engineer in two ways
● If the soil used for making building material
● If the soil on which structure is standing
1. Internal Sources:
This is more rare but, originates from such
concrete- making materials as hydraulic
cements, fly ash, aggregate, and admixtures.
● portland cement might be over-sulphated.
● presence of natural gypsum in the aggregate.
● Admixtures also can contain small amounts of
2. External Sources:
External sources of sulphate are more common and usually
are a result of high-sulphate soils and ground waters, or can
be the result of atmospheric or industrial water pollution.
●Soil may contain excessive amounts of gypsum or other
●Ground water be transported to the concrete foundations,
retaining walls, and other underground structures.
●Industrial waste waters.
● Sulphate attack is a chemical breakdown mechanism
where sulphate ions attack components of the
● The compounds responsible for sulphate attack are
water-soluble sulphate-containing salts, such as
alkali-earth (calcium, magnesium) and alkali (sodium,
potassium) sulphates that are capable of chemically
reacting with components of concrete.
What happens when sulphates get
It combines with the concrete paste, and begins
destroying the paste that holds the concrete
together. As sulphate dries, new compounds are
formed, often called ETTRINGITE .
These new crystals occupy empty space, and as
they continue to form, they cause the paste to
crack, further damaging the concrete.
C3A.Cs.H18 + 2CH +2S+12H = C3A.3CS.H32
C3A.CH.H18 + 2CH +3S + 11H = C3A.3CS.H32
● Main factors affecting sulfate attack:
1. Cement type and content:
The most important mineralogical phases of cement that affect the intensity
of sulphate attack is: C3A
2. Fly ash addition:
The addition of a pozzolonic admixture such as fly ash reduces the C3A
content of cement.
3. Sulphate type and concentration:
The sulphate attack tends to increase with an increase in the concentration
of the sulphate solution up to a certain level.
Control of sulphate attack:
The quality of concrete,
specifically a low permeability,
is the best protection against
● Adequate concrete thickness
● High cement content
● Low w/c ratio
● Proper compaction and curing
WATER SOIL EXTRACT
● Water soil extract can be said solution of
soil in water.
● Test is performed for soils where water
table is high.
● APPARATUS :
➔ Drying oven.
➔ Balance, readable to .001g.
➔ Test sieves
➔ 500 ml glass beakers
➔ 500ml conical flasks
➔ Electric hot plate
➔ Whatman filter papers
➔ Measuring cylinders
➔ silica crucibles
● PREPRATION OF SOIL AND ITS ACID
➔ Soil is prepared according to the BS 1377-3:1990
➔ Minimum mases of soils required are as follows:
fine grained soils : 100g
medium grained soils : 500g
coarse grained soils : 3Kg
➔ DRYING OF SOIL :
a) oven drying
b) air drying
PREPRATION OF TEST SPECIMEN
● Divide the material passing the 2mm sieve,
to produce a sample weighing
approximately 100 g.
● Pulverize the sample so that it passes the
425micron test sieve. Take about 60 g of
sample from the soil that is retained in pan.
● Again dry the sample at a temprature of 75º
to 80º C.
● Allow the specimen to cool to room
temperature in the dessicator.
PREPARATION OF WATER SOIL
● 2:1 water soil extract is to be made to
find the sulphate contents from the
● Weigh a sample of 50g. And transfer it
to a clean extraction bottle or beaker.
● Add exactly 100ml of distilled water to
the extraction bottle.
● If extraction bottle is to be used we must
use shaker to agitate for 16hours.
● If beaker is used then flocculator is to be
used to shake the sample.
● Filter the soil suspension into a clean and dry
flask through a suitable filter paper e. g.
Whatman no. 50.
● Transfer 50ml of filtereed extract to a 500ml
● Add distilled water about 300 ml.
● Prepare a barium chloride 5%(m/v) solution by
dissolving 50g of barium chloride in 1L of water.
● Test the solution for acidity with litmus paper and if
necessary make slightly acidic by the addition of
20 drops of hydrochloric acid.
● Bring the solution to the boil and add 10mL barium
chloride solution drop by drop with constant
stirring. Continue boiling gently until the precipitate
is properly formed.
● Allow the solution to stand at just below the boiling
point for at least 30 minutes, then leave to cool to
● Transfer the precipitate with extreme care to a
suitable filter paper e. g. Whatman no. 42 in glass
filter funnel and filter.
● Now transfer the filter paper and precipitates to a
previously ignited and weighed crucibles.
● Place the crucible and its contents in a muffle furnace
at the room temperature and gradually raise the
temperature to red heat. Ignition for about 15 minutes
at red heat is usually sufficient.
●Cool the crucibles to the room temperatures
using desiccator and weigh it to the nearest
●Calculate the mass of the precipitate from the
increase in the recorded mass of the crucibles.
● Sulphate content can be expressed either in
terms of the concentration of sulphate in the
extract as so3 of in g/L, or in terms of percentage
as so3 of water soluble sulphate in the soil
Calculate sulphate in g/L of the 2:1 water-soil
extract from the equation :
Concentration of sulphates so3
= 6.86 * m4 g/L
Where m4 is the mass of ignited precipitate in g.
Calculate the sulphate content as a percentage of
the soil from the equation:
water soluble sulphate content as SO3
= 1.372 * m4 (%)
Where m4 is the mass of ignited precipitate in